1. Field of the Invention
This invention relates generally to a method and apparatus for spreading rivets. More particularly, but not by way of limitation, the present invention relates to a precision bucking bar which controls the shape and the thickness of the butt of a rivet as it is spread to improve the quality of the riveting operation.
2. Background
Riveting is a common method for fastening sheet metal. In a typical riveting operation, a hole is drilled through multiple layers of sheet metal to be joined, a rivet of appropriate diameter and length is inserted through the hole, then the shank end of the rivet is spread so that the rivet is retained in the hole by its head on one side of the joint and by the spread shank, or butt, on the other side of the joint. Numerous methods are available for spreading rivets but primarily, squeezes are used where access permits, and a riveter, or driver, is used in conjunction with a bucking bar where access is not appropriate for using squeezes.
A bucking bar is basically a metal anvil which is placed against the end of the shank of a rivet. Typically, a flat surface of the bucking bar interfaces a flat end of a rivet shank. The head of the rivet is then xe2x80x9chammeredxe2x80x9d by a driver, thereby causing the shank to spread against the bucking bar. To produce a properly shaped butt of proper thickness, prior art bucking bars have required a skilled operator. Failure of the operator to hold the bucking bar square against the rivet shank will result in misshaped butts and bad rivet resulting in costly rework. Furthermore, prior art bucking bars are prone to wandering during the spreading operation and occasionally wander off the shank, likewise resulting in a bad rivets and subsequent rework.
Bucking bars are available in a variety of shapes and sizes to accommodate various obstacles which potentially interfere with a spreading operation.
Previous attempts have been made to develop a precision bucking bar which will produce a consistent butt regardless of operator skill. Such bucking devices suffer from a number of limitations. For example, they have universally required a relative large space behind the rivet, a luxury not available in many installations; they have not been available in a variety of geometries to avoid nearby obstacles; and they have not been of a conventional shape or size and thus have not felt familiar to an experienced operator. Hence, prior art precision bucking bars have not been well received in the field.
A second method for spreading a rivet employs an apparatus commonly known as xe2x80x9csqueezes.xe2x80x9d Squeezes typically include a pair of removable anvils, or points, a first point shaped to receive a rivet head, and a second provides a flat surface to interface the flat end of a rivet shank. To spread a rivet with a pair of squeezes, the rivet must be close enough to the edge of the workpiece for the squeezes to reach the rivet. The rivet is placed in a hole through multiple layers of sheet metal to be joined, the anvils are placed against each end of the rivet, and the operator squeezes the handle together to produce a compressive force between the head of the rivet and the end of the shank, thereby causing the rivet to spread. Automatic squeezes are also available wherein the points are pressed towards each other by a pneumatic or hydraulic actuator. As with driving a rivet, producing a quality butt requires the operator to maintain a consistently square angle between the face of the flat anvil and the rivet shank. Producing a consistent, quality butt requires an experienced operator.
Common to either type of spreading operation, a properly shaped butt of consistent thickness is essential to achieving maximum strength of the riveted joint. An improperly shaped butt may be too weak to hold under expected stresses or may concentrate stress in a small area resulting in failure of the workpiece.
It is thus an object of the current invention to provide a precision bucking bar which will consistently spread a rivet to form a butt of uniform thickness, regardless of operator skill level, and which may be produced in traditional shapes and sizes to accommodate rivets in a variety of installations and to provide a xe2x80x9cnaturalxe2x80x9d feel to an experienced operator.
It is a further object of the present invention to provide squeeze points which will produce a properly shaped rivet butt of consistent thickness and shape regardless of operator skill level.
These and other objects and advantages are achieved in a precision bucking bar whereon is provided one or more slots of a precise depth to produce a rivet butt of consistent shape and consistent thickness regardless of the skill level of the operator. By controlling the shape and thickness of the butt, a rivet may consistently be spread within engineering specifications, thereby ensuring each rivet will perform as intended and not transfer applied stresses to adjoining rivets.
In contrast to conventional bucking bars which provide only a flat surface, the degree to which the precision bucking bar can xe2x80x9cwanderxe2x80x9d during the spreading operation is limited by the edges of the slot produced thereon.
The inventive device is of a conventional shape and size to appeal to the experienced operator, to eliminate any need to retrain, and to allow use in any installation where a conventional bucking bar may be used.
In another embodiment, there is provided squeeze points for conventional squeezes which include, on the shank point, a slot or dimple of precise shape, depth and size to properly shape the butt of a rivet during the spreading operation.
A better understanding of the present invention, its several aspects, and its objects and advantages will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the attached drawings, wherein there is shown and described the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the invention.